On Mar 15, 2005, at 2:43 PM, Gene Bigham wrote:
> Micarta insulator material?
> I posted recently that I have ordered the tank components for my Henry
> 2K Classic X and they are in shipping to my address at this time. My
> question is this: I disassembled the band switch with its associated
> band plate tuning capacitors, which are progressively added in as you
> lower the band frequency. These are switched in by the band switch
> assembly adding capacitors thus capacitance as you lower the frequency
> selected. The plate is dipped with the roller inductor on this
> amplifier, not a variable capacitor.
> Having said that, I noticed that the insulator material (named Micarta
> by Henry - black material with what looks like fibers running through
> it) on the band switch is discolored on the end nearest the front of
> the amp. So is the associated band switch mounting hardware (all
> metal is at ground potential) attached to this insulator. This
> appears to be a place where arcing occurs. My immediate solution was
> to reverse the insulator in all the hardware mountings so the
> discolored portion was now at the rear of the amplifier instead of
> near the front.
IMO, the solution is to discourage regeneration at approx. 95MHz by
decreasing the Q of the VHF suppressors - which in turn lowers anode-Rp
and decreases VHF amplification. A high VHF-Q suppressor makes about
as much sense as a shock-absorber with almost no dampening. Henry
Radio Co. has a Long tradition of using high VHF-Q "parasitic
suppressors" . . . and not using their noggins.
Gene -- If you need some Micarta, I have 0.25" thick msterial. The
color is red.
> I tuned and loaded the amp into my 50 ohm PalStar dummy load and as I
> approached the top end of the output I heard some distinct frying
> happening again. I lower input power to the amp and this frying sound
> diminished and finally quit just as I was unkeying the driver stage.
> Opening the amplifier up I see the fresh end of the insulator material
> is now also slightly discolored and the metal mount has a discolored
> mark on it as well. There was an arc between the lower portion of the
> last doorknob capacitors (two in parallel) to the mount.
> Have any of you other Henry owners experienced this problem in the
> band switch area? If so can you advise any solutions you have
> explored and their outcomes?
> It looks to me that the mount itself has a bit of a sharp corner on
> it, the metal mounting flange that attaches to the insulator material,
> and from that sharp point it is arcing across the insulating material
> to the last contact on the band switch which is connected to the lower
> portion of two 75pf caps in parallel for 80 meters.
> By the way this happened on 40 meters so the last two caps were not
> even selected by the bandswitch.
> My proposed solution is to cut off the upper portion of the metal
> mount in this area so there is a larger distance between ground and
> the bottom of those two caps, that way there is not an easy
> opportunity to make the one quarter inch(? approx value I did not
> measure it) jump that the contact and the mount is providing right
> now.
> OK solutions other than that proposed? Do not want to fry a new band
> switch assembly right away!
> I also have a new roller inductor arriving with these parts and want
> to refurbish the old one which itself has some frying issues of its
> own. Will post on that later on.
> Thank you
> Gene Bigham
> KB0GU
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>
Richard L. Measures, AG6K, 805.386.3734. www.somis.org
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